With the diversification of services and increases in speed and capacity of ATM networks in recent years, it has become necessary to enhance the performance, functionality, and reliability of the ATM exchange system. In many services that ATM networks provides, PVCs (Permanent Virtual Channels) with the party and band semi-fixed are widely used. Under such circumstances, there has been an increasing demand for enhancement of the reliability of the PVC connections.
In order to avoid the breakage of a PVC connection due to a malfunction of the section lines or apparatus, it is considered effective to have a redundancy construction (duplexing, (n+1)-multiplexing) of the section lines in terms of the hardware. This construction, however, becomes complex to maintain and, therefore, the enhancement of the maintainability is lost. As a result, to enhance reliability and maintainability, it is necessary to take measures based on the use of software processing.
Special importance is placed upon how, at the time of a malfunction of the lines, communication should continue to be made with the least amount of cell loss in the PVC connection.
With reference to FIG. 4, an explanation will now be given of such a bypass route setting that is performed through a plurality of ATM exchangers. As illustrated, a master connection 100 that is used as an ordinary communication connection is set between an ATM exchanger 10 and an ATM exchanger 30, and, between the ATM exchangers 10, 20, and 30, there are set bypass connections 200.
The ATM exchangers are each equipped with cell header translators (HT) for each of the input/output section lines.
As a system of routing data to a bypass route which uses software processes, there is a system of switching as shown in FIGS. 1, 2, and 3.
FIG. 1 concerns the ATM exchanger 10 that is used in the network illustrated in FIG. 4. And, FIG. 1 is a view illustrating a state that prevails when in the ATM exchanger 10 there have been distributed PVC connections, the identifiers of which are different from the VPI/VCI of the master connection 100. Namely, FIG. 1 is a view illustrating the setting of the PVC connections by the conventional ATM exchanger.
FIG. 2 is a view, corresponding to the conventional technique, illustrating the flow of cells that, at the time of a malfunction, occur with respect to a bypass connection. FIG. 3 is a view illustrating a state that prevails when the flow of cells that has been bypassed is switched back to the original master connection.
As illustrated in FIG. 1, in the ATM exchanger 10 that is in an ordinary state of operation, the cell that has been received by a cell header translator 1A, by the translated header information is being referred to, is switched within the ATM exchanger 10 to an appropriate route. Then, the cell is output to the master connection through a cell header translator 1B. In this case, assume that a malfunction of the master connection is detected and that, in the ATM exchanger, setting is performed of a bypass connection. At that time, in the ATM exchanger, it was needed to newly set a bypass PVC connection, the VPI/VCI value of which is different from that of the master connection that has malfunctioned. In addition, in the operation of switching to a bypass route or switching back in FIGS. 2 and 3, transfer of data cells is done using a VPI/VCI value that is different from that which has been so far used for communication. So, there was the problem that interruption of data flow, etc. occurred.
Especially, in such a case as where the bypass route is constructed via a plurality of ATM exchangers, as one countermeasure, it may be considered effective to set connection information for use on a bypass route with respect to every one of the ATM exchangers on the bypass route beforehand. Or, there may be set beforhand a connection having another PVC number. Even in that case, it is necessary that the fact that the PVC used on the master connection has been changed over to a PVC for bypass owing to the occurrence of a malfunction, be recognized by each ATM exchanger or a user's side terminal. As a consequence, there was the problem that management of the information became complex.
Also, the invention described in Japanese Patent No. 2982784 discloses the following technique with regard to an ATM exchanger management system. The technique is that, in the case where a malfunction has occurred on the transmission path between the ATM exchangers that adjoin with each other via the transmission path in between, the cell is sent out using a spare transmission path or bypass route. By adopting this countermeasure, the technique aims to restore the ATM service quickly.
In this technique, the ATM exchangers that have been connected to one another via a plurality of transmission paths are each set in units of a section line. And, the ATM exchanger management system thereof includes input-side header translators (header-translators incoming) and output-side header translators (header-translators outgoing) each of which has PVC information of its relevant section line. That system further includes a PVC function management portion which, according to a request sent from the NMS, issues a request to set an ordinary PVC, to set a bypass PVC, and to switch to a bypass route. The portion, in addition, saves the ordinary PVC and bypass PVC information that has been thus set.
The PVC function management portion is directed, when performing a switch between an ordinary route and a bypass route, to perform re-setting of the ordinary PVC and bypass PVC according to the saved ordinary PVC information and bypass PVC information.
Namely, in the above-described conventional technique, there is disclosed the method of setting a bypass that is for a transmission path having malfunctioned between two of the ATM exchangers that are connected to one another via a plurality of transmission paths. However, in an ordinary state of operation, there is a case where a malfunction occurs on each of the adjoining ATM exchangers. In this case, the above-described system of setting a bypass itself has the difficulty of being operated. As a result, it is more highly demanded that the quality of and the reliability of the communication at a level of network be guaranteed.
Also, in actuality, in a large-scale communication carrier, in a wide range of area there are disposed a plurality of (three or more) ATM exchangers, each of which is performing its exchange/transfer processes of communication information in the area where it is disposed. However, despite the ability of, at a level of network, using a plurality of communication section routes, in the above-described conventional technique, because setting of a bypass route is limited to the two exchangers, the following problem arises. Namely, regarding the PVC performing communication with use of the two exchangers that have malfunctioned, providing any service becomes impossible.